I'll answer to the best of my knowledge
why is phpbb 2.2 using HTML as the template files insted of .tpl or .php?
Some syntax highlighting editors didn't like .tpl files and didn't show syntax highlighting in .tpl files. Also, people are more familiar with a .html extension and are more likely to assoiciate it with templates than a .tpl extension.
also is there anyway for me to convert the html files to php? cause the html files wont show up in firefox only IE?
No. The way the templating system works, the files must be .html files
Also why does the admin section use php and not the overall styles?
Because in phpBB 2.0.x, people didn't change the admin templates (which was why it was done in the first place), therefore the [redundant] files are wasting disk space.
Anyways i love the whole ease of use with the styling system
phpbb 2.2 is gonna be amazing